Gold(i) mercaptocarboxylic acid esters, method of their preparation and use

ABSTRACT

Novel gold(I) mercaptocarboxylic acid esters of the formula (I) ##STR1## in which X is a C 1  -- to C 3  alkylene group and Z is a group from the series tricyclo(5,2,1,0 2 .6)decane-8- or -9-yl or tricyclo (5,2,1,0 2 .6)decyl-3- or -4-methyl. These esters can be prepared from mercaptocarboxylic acid esters of the formula (II) ##STR2## and from a gold(I) chloride-dialkylsulfide complex. The novel esters can be used in gold preparations for gilding solid bases, especially ceramic materials. Compared to known gold(I) mercaptocarboxylic acid esters, the novel esters result in considerably shorter drying times for gold preparations.

BACKGROUND TO THE INVENTION

The present invention relates to novel gold(I) mercaptocarboxylic acidesters which are characterized by a tricycloalkyl group in the alcoholcomponent of the ester. The present invention also concerns a method ofpreparing these new gold mercaptides and their use in gold preparationsfor gilding solid bases.

So-called gold preparations have long been used to apply a golddecoration onto ceramic articles and to produce strip conductors of goldin integrated circuits. Such preparations generally contain one orseveral sulfur-organic gold compounds soluble in an organic carriermedium, fluxing agents such as e.g. resinates of one or several of theelements B, Si, V, Cr, In, Sn, Sb, Bi, and Rh, and the carrier mediumcontains a resin and organic solvent. The gold preparations are appliedonto the surface to be coated and after the evaporation of the solvent,a burning process follows at a temperature adjusted to the substrate andthe gold preparation, during which the gold film is formed and fixedwith good adhesion to the surface.

The sulfur-organic gold compounds have long been almost exclusivelyso-called gold sulforesinates which were obtained from a gold salt andsulfurized terpenes, especially naturally occurring terpenes. Onedisadvantage of these sulforesinates is that their preparation isassociated with naturally occurring raw materials whose supply islimited and whose quality is subject to variations. In order toeliminate these disadvantages, and at the same time influence theproperties of the gold preparations in a purposeful manner, purelysynthetically prepared gold(I) mercaptides with very differentstructures have been used in the gold preparations.

German patent 12 86 866 teaches defined, secondary gold(I) mercaptideswith the formula RR'CH-S-Au in which R and R' signify alkyl, cycloalkyl,aryl or alkylaryl. The use of these gold(I) mercaptides required the useof strongly polar solvents such as nitrobenzene. Tertiary gold(I)mercaptides with the formula RR'R"C-S-Au with R, R' and R" equal toalkyl are soluble according to DE-AS 12 98 828 in slightly polarsolvents (e.g., toluene); in addition, these mercaptides exhibit lowerdecomposition temperatures. Finally, aromatic gold(I) mercaptides withthe formula Ar-S-Au have also been suggested for gilding preparations(German patent 12 84 808). A bicyclic mercaptide, namely gold(I) bornylmercaptide (U.S. Pat. No. 4,221,826), proved to be advantageous for theproduction of integrated electronic circuits. The above-named gold(I)mercaptides have the disadvantage of a partially very unpleasant odorwhich becomes particularly noticeable in a disturbing manner when thegold preparations are applied by heat (e.g., by means of hot screenprinting).

DE-AS 12 92 463 teaches argentiferous (i.e., silver containing) gildingpreparations containing a coordination compound consisting of a gold(I)mercaptide and an equimolar amount of a silver carboxylate or silvermercaptide. Primary or secondary alkyl- or alkylarylmercaptides and alsogold(I) mercaptides of 2-methoxyethyl-, ethyl-, isooctyl- andtert.-dodecylthioglycolate are described as the gold(I) mercaptide.These coordination compounds are distinguished by greater solubility andbetter coating power in comparison to the individual compounds. Thecoordination compounds have the disadvantage that silver compounds areobligatorily present in equimolar amount and the creation of thedecoration is thus limited in regard to the color. Moreover, thedecorations are very susceptible to tarnishing phenomena due to the highsilver content.

The family of gold(I) thioglycolic acid esters has a considerably morepleasant odor than the above-mentioned gold(I) mercaptides free ofcarboxyl groups.

Of the gold(I) thioglycolic acid esters cited in DE AS 12 92 463, onlygold(I) isooctylthioglycolate and gold(I) tert.-dodecylthioglycolate arebasically suitable (in the absence of a stoichiometric amount of asilver compound) for use in gilding preparations in which a goldcompound soluble in organic solvents is required (e.g., in bright goldpreparations). Gold(I) ethylthioglycolate andgold(I)-2-methoxyethylthioglycolate are compounds which are almostinsoluble in organic solvents.

However, as Applicants determined, the previously named isooctyl- andtert.-dodecyl-gold(I) thioglycolates are not satisfactorily suitable ingilding preparations, especially for the decoration of ceramicmaterials, because the drying time of the preparations is very long.This has a very negative influence on the economy of the decoration.

SUMMARY OF THE INVENTION

An object of the present invention is the development of gold(I)mercaptides which have less odor than the customary mercaptides withoutester function and, in addition, a lower solvent retention in goldpreparations of a customary composition, thus resulting in a shorterdrying time than is the case with known thioglycolates.

According to the present invention, this and other objects are achievedby means of gold(I) mercaptocarboxylic acid esters of the formula##STR3## in which X represents an alkylene group and Z an alkyl group inwhich X is a C₁ --to C₃ alkylene group and Z is a group from the seriestricyclo(5,2,1,0².6) decane-8- or -9-yl or tricyclo (5,2,1,0².6)decyl-3-or -4-methyl.

DETAILED DESCRIPTION OF THE INVENTION

The novel gold(I) mercaptides of the present invention are derivativesof mercaptoacetic acid, 2- and -3-mercaptopropionic acid, 2-, 3- or4-mercaptobutyric acid, and 2- or 3-mercaptoisobutyric acid. On accountof their ready availability, products based on mercaptoacetic acid (alsocalled thioglycolic acid) and 2- or 3-mercaptopropionic acid arepreferred.

The alcohol component of the ester, which component forms the base ofthe gold(I) mercaptides of the present invention, can exhibit one of thefollowing structures: ##STR4##

Naturally, these alcohols can be present in the form of one of thepossible stereoisomers. However, mixtures of isomers (positional and/orstereoisomers) can be conveniently used for preparing the gold(I)mercaptides of the present invention and the novel substances are alsoaccordingly usually mixtures of isomers.

Especially preferred gold(I) mercaptides in accordance with the presentinvention are gold(I) mercaptoacetic acid (tricyclo(5,2,1,0².6)decyl-8or -9) ester, gold(I) mercaptoacetic acid-((tricyclo(5,2,1,0².6)-decyl)-3- or 4-methyl) ester, gold(I) 2- or 3-mercaptopropionicacid-(tricyclo(5,2,1,0².6)decyl-8 or -9) ester, and gold(I) 2- or3-mercaptopropionic acid-(tricyclo(5,2,1,0².6)decyl-3- or 4-methyl)ester. The novel substances can be identified by means of their chemicalanalysis and their melting point. The substances dissolve in thecustomary solvents (e.g., aromatic hydrocarbons) which are used incarrier media for gilding preparations.

The novel gold(I) mercaptides have broadened the palette of goldcompounds which are particularly well suited for use in goldpreparations. The special advantage of these novel gold(I) mercaptidesis the fact that the drying time is shortened to a fraction of thedrying time necessary for the closest previously known gold(I)mercaptoacetic acid esters. This shortening of the drying time, whichcan amount in individual instances to 90% or more, was unexpected andnot foreseeable. These novel gold(I) mercaptides have only a slight odorand thus pose no problems as regards the work environment. It ispossible to modify the properties of the gold(I) mercaptides by means ofthe selection and of the possibility of combining the X and Z groups andthus to adapt them more precisely to the desired use. Such an adaptationwas not possible in the case of the gold(I) bornyl mercaptides of U.S.Pat. No. 4,221,826.

The novel gold(I) mercaptides of formula I can be prepared in a knownmanner like that known for the preparation of previously known gold(I)mercaptides (U.S. Pat. No. 4,221,326; DE-AS 12 86 866; DE-AS 12 98 828).A gold(I) chloride-dialkylsulfide complex, obtainable in a known mannerby reacting an aqueous solution of tetrachloroauric acid with double thestoichiometric amount of a dialkylsulfide in the presence of water, isreacted with a mercaptocarboxylic acid ester of the formula ##STR5## (inwhich X and Z have the same meaning as in formula I) in a molar ratio ofabout 1 to 1 in the presence of an organic solvent at 0° to 40° C. Theorganic solvent should dissolve the ester of formula II but practicallynot dissolve the desired gold(I) mercaptide of formula I. The expression"a molar ratio of about 1 to 1" means that a slight excess, up to 10mole % of the ester of formula II, can be present; but a molar ratio of1 to 1 is preferred. One of the previously known dialkylsulfidecomplexes, the dimethyl- or diethylsulfide complex, is a potentialgold(I) chloride-dialkylsulfide complex which can be used as such or inthe form of the reaction mixture obtained when preparing this complex;however, it is preferable if the gold(I) methionine complex is used. Thegold(I) mercaptide of formula I precipitates during the reaction of thegold(I) chloride-dialkylsulfide complex with the ester of formula II. Itis quite easy, when using methylene chloride as organic solvent, toobtain a powdery product which can be washed acid-free in a simplemanner and which in particular does not contain any inclusions of thegold(I)-dialkysulfide complex and mercaptocarboxylic acid ester used.The actual reaction is followed by solid-liquid phase separation, then awash of the solid with water or aqueous solutions in order to remove thehydrogen chloride formed, and finally by drying. It is advantageous ifresidual water is removed before the drying by means of washing with amixture of methanol or ethanol and methylene chloride or anotherlow-boiling aliphatic chlorinated hydrocarbon. The drying preferablytakes place at temperatures below 50° C.

The esters of formula II can be obtained by means of customaryacid-catalyzed esterification methods from the mercaptocarboxylic acidsand the tricyclic alcohols of the previously named structures in thepresence of an azeotrope entraining agent. Toluene is an especiallysuitable entraining agent. A purification of the ester of formula II forpreparing the gold(I) mercaptides of formula I is generally notnecessary.

As has already been emphasized, the gold(I) mercaptocarboxylic acidesters of formula I can be used in gold preparations for gilding solidbases, especially those consisting of ceramic materials. The term "goldpreparations" denotes liquid to pasty preparations which are appliedaccording to various application methods (e.g., application by brush,spraying, indirect screen-printing (transfer pictures), or direct hot orcold screen-printing). The bases to be gilded must exhibit a sufficientthermal resistance in order to resist the burning process at which thegold film forms. The burning temperatures can be in a range ofapproximately 200° to over 1000° C., but in the case of ceramic surfacestemperatures in a range of 400° to 900° C. are preferred.

Gold preparations (compositions) for gilding ceramic materials (such asglass, glass ceramic, porcelain, and other silicatic or non-silicaticceramic materials) also contain a fluxing agent and an organic carriermedium of resins and solvents in addition to the soluble gold compound.Moreover, other auxiliary processing substances as well as substancesinfluencing the appearance and the properties of the gold film, such asother soluble noble-metal compounds, gold powder and glass frits, can becontained in the gold preparations. The gold content in the goldpreparations suitable for decorative purposes as well as for technicalpurposes (such as printed circuits and lamp reflectors) can be withinbroad limits. So-called bright gold preparations usually contain 8 to12% gold in the form of one or several gold(I) mercaptides; burnishedgold preparations usually contain elementary gold in addition to thegold compounds (total gold content usually 15 to 40% by weight). Anotherclass of gold preparations for which the gold(I) mercaptides of formulaI can be used are the so-called gold luster preparations which containonly a low amount of gold (a few % by weight) but contain more goldfluxing agent along with the gold and do not comprise a cohesive goldfilm but rather a decoration with a characteristic golden luster.

The fluxing agents are like those initially cited and described in moredetail in the documents cited above, that is, in particular,sulforesinates, resinates, naphthenates, carboxylates, anddithiocarbamates of the elements B, Si, V, Cr, In, Sn, Pb, Sb, Bi, andRh. Typical carrier media contain one or several organic solvents fromthe series of ketones, aromatic and aliphatic hydrocarbons, aliphaticchlorinated hydrocarbons, alkyl acetates, glycol ethers, terpenehydrocarbons, and ethereal oils, as well as waxes in the case of mediafor hot screen-printing, and contain one or several resins from theseries of wood resins (e.g., colophonium- and dammar resin) andsynthetic resins (e.g., hydrocarbon resins, polyacrylates, andpolymethacrylates). Typical bright gold preparations for screen-printingcontain 20 to 30% by weight of the gold(I) mercaptides of the presentinvention, as pure compound or mixture of isomers, fluxing agent (s),especially mixtures of Cr-, Bi- and Rh resinates in an amount of 0.1 to0.5% by weight calculated as chromium oxide, bismuth oxide and rhodiummetal, and 65 to 80% by weight carrier medium (approximately a fourth ofwhich is resins).

The drying speed of the gold preparation, under the same externalconditions (temperature, pressure, and relative atmospheric humidity),is a function of the absolute evaporation speed of the solvent present,the extent of solvent retention by the organic components of thepreparation, and also of the gold (I) mercaptide used. It turned outthat, without adversely affecting the desired processing properties of apreparation, which are essentially determined by the type of carriermedium, the drying properties are influenced to an unexpectedly greatextent by the structure of the organic gold compound. The structure ofthe substances of the present invention results in extraordinarily shortdrying times in comparison to previously known substances with a similarstructure (see examples 3 and 4 and reference examples 1 and 2). Thedrying times are approximately the same within the group of thesubstances of formula I.

Determination of the drying time: Surfaces of 5×5 cm are printed withthe gold preparation (screen-printing); the surface is coated withsea-shore sand at intervals of one half to one hour; the drying processis over when the sand falls off, due to insufficient adhesion, when thesanded surface is vertically positioned.

EXAMPLE 1 Preparation of the mercaptocarboxylic acid esters of formulaII

Reaction of mercaptocarboxylic acid with3(4)-hydroxymethyl-tricyclo(5,2,1,0².6)decane:

1.2 moles 98% mercaptoacetic acid (112.7 g) and 1 mole 3(4)-hydroxymethyl-tricyclo(5,2,1,0².6)decane (166.0 g) (isomeric mixture"TCD-Alkohol M" by Hoechst) dissolved in 250 ml toluene are heated inthe presence of 2 g p-toluene sulfonic acid on a water separator underreflux (approximately 120° C.). After approximately 2.5 h, thetheoretical amount of water (18 ml) has been separated. After havingcooled off, the reaction mixture is neutralized, for the separation ofthe excess mercaptoacetic acid, with 10% by weight sodium hydroxidesolution (approximately 80 ml) under agitation (approximately 30 min.).The aqueous phase is separated and the toluene distilled off underreduced pressure (15 mbars, 40° C. to 120° C.). 247.5 g of a colorlessliquid with a residual toluene content of 3% by weight remain. Thereaction takes place quantitatively. The raw mercaptoaceticacid-(tricyclo(5,2,1,0².6)decyl)-3(4)methyl)ester is reacted furtherwithout further purification.

Identification: ¹ H-NMR spectra

Further products of formula II were prepared in basically the samemanner using the particular mercaptocarboxylic acid and the above-named"TCD-Alkohol M" or 8(9)-hydroxytricyclo(5,2,1,0².6)decane (isomericmixture "TCD-Alkohol A" by Hoechst).

EXAMPLE 2 a) Preparation of gold mercaptoaceticacid-(tricyclo)5,2,1,0².6)decyl-3(4)methyl)-ester

1 mole gold in the form of an aqueous solution of tetrachloroauric acid(38% by weight Au) (518.5 g) is added drop by drop within one hour intoa suspension of 2 moles D,L methionine (298.4 g) and 2 liters water. Thetemperature is maintained at 0° to 5° C. by external cooling. After theend of the reduction, the gold(I) chloride-D,L-methionine hydrochloridecomplex is present partially in a dissolved form and partially asprecipitate. 1 mole of mercaptoaceticacid-(tricyclo(5,2,1,0².6)decyl)-3(4)-methyl)-ester (240.1 g) mixed with250 ml dichloromethane and 250 ml ethanol is added drop by drop at atemperature of 5° to 15° C. within one hour to this suspension. Goldmercaptoacetic acid-(tricyclo(5,2,1,0².6)decyl-3(4)-methyl)-esteraccumulates as white precipitate which is filtered off immediately afterthe drop-by-drop addition. The precipitate is agitated for purificationfor 30 min. in 0.8 liter dichloromethane, compounded with 1.5 litersethanol, agitated for 15 min. and removed by suction. The raw product isthen agitated 30 min. with 450 g 3% sodium hydrogen carbonate, removedby suction and washed on a filter with 500 ml water. The raw product isagitated again 30 min. in 0.8 liter dichloromethane, compounded with 1.5liters ethanol, agitated 15 min. and removed by suction. The raw productis dried in thin layers at 50° C. for 24 hours. The yield is about 98%relative to gold used.

Melting point: 172° C.

    ______________________________________                                        Analysis:   Au     C          H    S                                          ______________________________________                                        calc.:      45.14  35.79      4.39 7.35                                       obs.:       44.92  35.68      4.32 7.30                                       ______________________________________                                    

The following gold mercaptides were prepared in a manner analogous tothat described in example 2 from the corresponding mercaptocarboxylicacid esters:

    ______________________________________                                         ##STR6##                                                                     Melting point:                                                                             108° C.                                                   Analysis:    Au      C         H    S                                         calc:        43.74   37.34     4.70 7.12                                      obs.:        43.68   37.40     4.68 7.11                                       ##STR7##                                                                     ______________________________________                                    

Au (theoretical): 46.64%

Au (experimental): 46.48%

Melting point: 138° C. ##STR8## Au (theoretical): 45.14% Au(experimental): 44.91%

Melting point: 97° C.

EXAMPLE 3 AND REFERENCE EXAMPLE 1

Bright gold preparations (according to the present invention and to thestate of the art)--compositions (data in % by weight) and drying times(hours):

    ______________________________________                                        A     54.13    24.39  gold mercaptoacetic acid-                                              29.74  (2-ethylhexyl)-ester in mesitylene                      B     54.13    26.55  gold mercaptoacetic acid(tricyclo                                      27.58  (5,2,1,0.sup.2.6)decyl)-3(4)-methyl-                                          ester in mesitylene                                     C     1.00     rhodium sulforesinate in terpeniol, 5% Rh                            1.00     bismuth resinate in terpeniol, 7% Bi.sub.2 O.sub.3                   1.50     chromium resinate in terpeniol, 3% Cr.sub.2 O.sub.3                  20.00    sulfurized colophonium resin                                         22.37    mesitylene                                                     ______________________________________                                    

The mixtures of A plus C (reference example 1) and B plus C (example 3)were applied onto glass plates by screen-printing (polyester screenfabric "110 T" 110threads per cm., medium heavy).

The drying took place at 20° C. and a relative atmospheric humidity of60%.

The bright gold paste consisting of components A and C required a dryingtime of 26 hours.

The bright gold paste consisting of components B and C (in accordancewith the present invention) required a drying time of only 2 hours.

EXAMPLE 4 AND REFERENCE EXAMPLE 2

Bright palladium preparations (in accordance with one present inventionand the state of the art)--composition (% by weight) and drying times(hours)

    ______________________________________                                        A     50.32    20.32  gold mercaptoacetic acid-                                              30.00  (2-ethylhexyl)-ester in mesitylene                      B     50.32    21.44  2-gold mercaptopropionic acid-                                         28.88  tricyclo(5,2,1,0.sup.2.6)decyl)-                                              8(9))-ester in mesitylene                               C     1.00     rhodium sulforesinate in terpeniol, 5% Rh                            1.00     bismuth resinate in terpeniol, 7% Bi.sub.2 O.sub.3                   1.50     chromium resinate in terpeniol, 3% Cr.sub.2 O.sub.3                  6.30     palladium sulforesinate in terpeniol, 8% Pd                          5.00     silver sulforesinate, 20% Ag                                         17.00    sulfurized colophonium resin                                         17.88    mesitylene                                                     ______________________________________                                    

The mixtures of components A plus C (reference example 2) and B plus C(example 4) were applied in accordance with example 3/reference example1 by screen-printing and the drying time determined.

Reference example 2: Drying time 18 h

Example 4: Drying time 1 h

Further variations and modifications of the invention will becomeapparent to those skilled in the art from the foregoing and are intendedto be encompassed by the claims appended hereto.

German Priority Application P 40 40 446.3, filed on Dec. 18, 1990, isrelied on and incorporated by reference in its entirety.

What is claimed:
 1. A gold(I) mercaptocarboxylic acid ester of theformula ##STR9## in which X is an alkylene group and Z an alkyl group,wherein X is a C₁ -- to C₃ alkylene group and Z is selected from thegroup consisting of tricyclo(5,2,1,0².6)decane-8- or -9-yl andtricyclo(5,2,1,0².6)decyl-3- or -4-methyl.
 2. The gold(I)mercaptocarboxylic acid ester according to claim 1, wherein X is CH₂ orCH(CH₃).
 3. The gold(I) mercaptocarboxylic acid ester according to claim1, wherein said ester is selected from the group consisting of gold(I)mercaptoacetic acid (tricyclo(5,2,1,0².6)decyl-8 or -9) ester, gold(I)mercaptoacetic acid-((tricyclo(5,2,1,0².6)-decyl)-3- or 4-methyl) ester,gold(I) 2- or 3-mercaptopropionic acid-(tricyclo(5,2,1,0².6)decyl-8 or-9) ester, and gold(I) 2- or 3-mercaptopropionicacid-(tricyclo(5,2,1,0².6)decyl-3- or 4-methyl) ester.
 4. The gold(I)mercaptocarboxylic acid ester according to claim 1, prepared by a methodcomprising reacting a gold(I) chloride-dialkylsulfide complex with amercaptocarboxylic acid ester of the formula ##STR10## in which X is aC₁ -- to C₃ alkylene group and Z is selected from the group consistingof tricyclo(5,2,1,0².6)decane-8- or -9-yl andtricyclo(5,2,1,0².6)decyl-3- or -4-methyl, in a molar ratio of saidester to said complex of about 1:1 to about 1.1:1 in the presence of anorganic solvent at 0° to 40° C.
 5. The gold(I) mercaptocarboxylic acidester according to claim 4, wherein said ratio is 1:1.
 6. The gold(I)mercaptocarboxylic acid ester according to claim 4, wherein said complexis selected from the group consisting of dimethylsulfide complex,diethylsulfide complex, and gold(I) methionine complex.
 7. The gold(I)mercaptocarboxylic acid ester according to claim 4, wherein said solventis methylene chloride.
 8. The gold(I) mercaptocarboxylic acid esteraccording to claim 4, wherein X is selected from the group consisting ofCH₂, CH₂ --CH₂ and CH(CH₃).
 9. The gold(I) mercaptocarboxylic acid esteraccording to claim 4, further comprising separating the resultingprecipitated gold(I) mercaptocarboxylic acid ester, washing said esterwith water, and drying said ester.
 10. The gold(I) mercaptocarboxylicacid ester according to claim 9, wherein said solvent is methylenechloride and further comprising removing water from said ester prior tosaid drying step by washing said ester with a mixture of (a) methanol orethanol and (b) methylene chloride or a low boiling aliphaticchlorinated hydrocarbon.